1. Field of the Invention
The present invention relates in general to an internal combustion engine, and more particularly to an engine cold starting control device.
2. Description of Related Art
To start an engine efficiently and effectively, the fuel/air ratio of a fuel charge delivered to the engine should be controlled both at the time of starting the engine (i.e, cranking the engine) and during the time the engine warms to its designed operating temperature.
When starting a cold engine, the fuel charge should contain a higher concentration of fuel (i.e., be "richer") because some percentage of the fuel will condense on the cool induction system of the engine before the charge is delivered to the combustion chamber. The initial ratio of fuel to air thus must be richer in order to supply a change having the proper fuel to air ratio. Of course, colder weather exacerbates this problem; with a lower starting temperature, a large percentage of the fuel in the charge condensates on the colder surfaces of the induction system.
Conventional charge formers use various types of cold starting devices to produce a richer charge when starting a cold engine. For instance, a choke valve is used in a conventional carburetor to decrease air flow into a mixture chamber of the carburetor, and consequently the concentration of fuel in the charge is increased.
In order to compensate for variable starting temperatures of the engine, it is known to adjust the choke valve to tailor the opening degree of the choke valve to the starting temperature of the engine. Colder starting temperatures require a smaller opening degree (i.e., less air flow) in order to produce a rich charge, and warmer starting temperatures require a larger opening degree (i.e., more air flow) to produce a less rich charge.
The engine warms after starting. Less fuel condensation occurs as the engine and its induction system warms, and consequently, the percentage of fuel in the fuel charge can be decreased. The fuel to air ratio desirably decreases at a rate corresponding to the rise in engine temperature to maintain consistency in engine performance. Thus, the fuel to air ratio of the charge gradually decreases to a designed ratio for operation after the engine has warmed.
Conventional cold start devices, which employ only a choke valve or a similar device, do not gradually decrease the fuel concentration level of the charge. These prior devices rather run richer than required under some operating temperatures and leaner than required under other operating temperature. As a result, engine efficient is sacrificed under some operating conditions and engine performance is sacrificed under other operating conditions.